A study of incident, clinically-diagnosed Alzheimer's disease is proposed in a biracial population of 9,800 persons 65 years of age and older living in a geographically defined area of Chicago. The study will test the following major hypotheses: (a) Incidence of clinically diagnosed Alzheimer's disease is higher among African Americans than among white Americans. (b) Incidence of clinically diagnosed Alzheimer's disease is higher among persons with lower educational attainment. (c) Incidence of clinically diagnosed Alzheimer's disease is lower among persons who smoke cigarettes than among comparable non-smokers. (d) Incidence of clinically diagnosed Alzheimer's disease is higher among women than men. In addition, the study will provide estimates of the age-specific incidence of clinically diagnosed Alzheimer's disease in this community, identify predictors of change in cognitive function over a three-year period in the population and, as a secondary goal, provide estimates of the age-specific prevalence of Alzheimer's disease. The study will have two major operational components, separated by three years; each component will have two similar stages. The first stage will be a population interview that contains brief performance tests of cognitive function. The second stage will be clinical evaluation for Alzheimer's disease of a random sample of participants, stratified by age, sex, race and first stage cognitive test performance. Persons with Alzheimer's disease may be identified from any stratum not merely from the poor performance group. The design permits risk factor information to be measured prior to the onset of overt disease. Standard diagnostic criteria will be used, evaluators will be blinded to sampling category and structured questionnaires and evaluation techniques will be used.